Fused coupler assembly

ABSTRACT

A fused coupler assembly includes a submersible conductive housing used in underground distribution systems. The housing contains a dielectric filler in which a cylindrical resistor shield encompassing a fuse element is located. The cylindrical shield is formed of a tube coated with a resistance material so that a shield is formed of sufficiently low resistance to prevent corona from occurring between the tube and the fuse element. The coating shield also is of sufficiently high resistance to minimize line-to-ground leakage when the fuse element is blown during a fault condition.

United States Patent [1 1 Vadnagara [451 Dec. 25, 1973 FUSED COUPLER ASSEMBLY [75] Inventor: Ramanlal R. Vadnagara, Chicago,

Ill.

[73] Assignee: Joslyn Mfg. and Supply Co.,

Chicago, L

[22] Filed: Sept. 10, 1969 21 App1.No.:856,691

no l2 Is 2s pa 3,376,541 4/1968 Link 174/73 3,513,425 5/1970 Arndt 337/201 FOREIGN PATENTS OR APPLICATIONS 479,211 2/1938 7 Great Britain 337/224 Primary Examiner-Harold Broome Att0rneyMason, Kolehmainen, Rathburn and Wyss 57 ABSTRACT A fused coupler assembly includes a submersible conductive housing used in underground distribution systems. The housing contains a dielectric filler in which a cylindrical resistor shield encompassing a fuse element is located. The cylindrical shield is formed of a tube coated with a resistance material so that a shield is formed of sufficiently low resistance to prevent corona from occurring between the tube and the fuse element. The coating shield also is of sufficiently high resistance to minimize line-to-ground leakage when the fuse element is blown during a fault condition.

1 Claim, 2 Drawing Figures [51] Int. Cl. H0111 85/02 [58] Field of Search 337/201, 224, 199; 174/73 [56] References Cited UNITED STATES PATENTS 2,216,661 10/1940 Dannenberg.... 337/224 2,660,644 11/1953 Murray 337/224 2,844,691 7/1958 Howell.... 337/224 3,318,995 5/1967 Buckley.. 174/73 3,344,391 9/1967 Ruete 174/73 1 FUSED COUPLER ASSEMBLY The present invention relates to a new and improved fuse, and particularly to a fused coupler assembly for use in an underground distribution system.

Fuse units are known for use with underground distribution systems which contain a silver fuse wire that will melt and vaporize when a fault condition appears and an overload current is carried by the fuse element. The fuse element is located within a dielectric inside a submersible conductive housing. Difficulty may be experienced with corona occurring between the fuse element and the dielectric encompassing it.

In accordance with the present invention, a conductive corona shield is placed in void-free engagement with the dielectric. When a fault occurs and a fuse is blown, the corona shield is subjected to line-to-ground voltage, and the corona shield must have a low enough resistance to substantially limit the corona, but a high enough resistance to prevent excessive line-to-ground leakage from occurring.

Accordingly, it is an object of the present invention to provide a new and improved fused coupler assembly for underground distribution systems.

Another object of the present invention is to provide a new and improved resistor tube within a fused coupler assembly defining a corona shield to prevent corona.

A further object of the present invention is to provide a new and improved fuse structure within a dielectric housing.

Briefly, the present invention relates to a new and improved fused coupler assembly particularly useful in underground distribution systems. The present fused coupler is an improvement over that shown and described in the copending patent application filed Aug. 15, 1967, by'Edward H. Yonkers, S. N. 660, 748. The coupler includes a conductive submersible housing containing a dielectric filler in which a cylindrical resistor shield encompasses a fuse element. The resistor shield is formed by coating a dielectric tube with a resistive shield to preclude corona effect between the tube and the fuse element and to reduce line-to-ground leakage that may occur when the fuse element is blown. To ensure void-free interfacial engagement between the coated resistor tube and the dielectric filler in the housing throughout the thermal operating range of the fused coupler, a layer of pliable material is disposed between the tube and the dielectric filler.

For a better understanding of the present invention, reference may be had to the accompanying drawings wherein:

FIG. 1 is a cross sectional view ofa fused coupler assembly according to the present invention; and

FIG. 2 is a side elevational view ofa resistor tube and its coating shield.

Referring now more specifically to FIG. 1 of the drawings, therein is illustrated a fused coupler assembly which is indicated generally as and which embodies the present invention. The fused coupler assembly 10 includes a conductive housing 12 in which is cast a center of hard dielectric filler 14. A cylindrical resistor tube 16 insulates a fuse element 18 that is encompassed by the tube 16. The fuse element 18 is of silver or other conducting material that will melt and vaporize into and over the surface of sand grains 20 which surround the fuse element 18. The fuse element 18 has its respective ends electrically connected to a pair of contact rods or plugs 22. The operation of melting and vaporization of such a fuse element 18 is well known and takes place so rapidly under fault conditions that the current is essentially cut off before it reaches the full value of the available fault current. Thus, when the fuse element 18 is melted, the circuit will become open and a load current is no longer carried by the fused coupler 10 between the contact rods 22.

In order to minimize the length required for a fuse of a given rating, the fuse element 18 is wound around a core 24 that contains a spiral groove 26 along its length. The core 24 maintains sufficient distance between the turns of the fuse element 18 to prevent hot ionized gas from shorting out the turns. A space 28 encompassing the core 24 within the resistor tube 16 is filled with the sand grains 20 of suitable refractory granules such as alumina or silica.

The resistor tube 16 is of suitable high strength refractory material, at least in its lining, to withstand internal pressures which may develop during operation. As illustrated in FIG. 2, the resistor tube 16 is coated with a helical winding 30 of high resistance material defining a corona shield in void-free interfacial engagement with the dielectric filler 14.

At either end of the tube 16 is a cylindrical contact ferrule 32 that electrically connects one of the contact rods 22 to an adjacent end of the fuse element 18. A pair of ferrule end caps 34 seals both ends of the resistor tube 16. The resistive coating 30 is connected near one or both of its ends by a conductive epoxy bond 36 to the line potential through the ferrule contacts 32. It was found that a charging current between the coating 30 and ground on the housing 12 produces a voltage drop along the resistive coating 30 so that a potential difference appeared between the coating 30 and the fuse element 18. In order to minimize any corona effect, the resistive value of the coating 30 must be limited to a proper value depending on the actual dimensions of the particular design of the fused coupler 10. On the other hand, if the resistive value of the coating 30 is not made sufficiently high, excessive line-toground leakage can occur when the fuse element 18 is blown. By selecting a resistor tube 16 with a high enough resistance, this leakage current is limited to safe values. A terminal-to-terminal resistance of the coating 30 in the range of 50 to 150 megohms was found satisfactory. In one commercial embodiment of an 8.3 kV fuse, a resistance of megohms was found satisfactory, limiting the line-to-ground current to 69 microamps at a power dissipation of 0.57 watts.

The fused coupler assembly 10 is subjected to a wide range of temperature during normal operating conditions of the underground distribution system. The current flowing in the fuse element 18 also tends to create a certain amount of heat within the enclosed resistive tube 16 causing the tube 16 to be subjected to additional radical changes in temperature. The dielectric filler l4 and tube l6'may have difi'erent coefficients of thermal expansion which may result in cracking of the filler 14 or in separating of the void-free interfacial contact between the dielectric filler l4 and the shield 16 when the assembly 10 is subjected to temperature changes. This difficulty is overcome by providing a layer of pliable material 38 such as urethane encompassing the resistor tube 16 and its corresponding coating 30. The layer of pliable material 38 is such that it has a coefficient of thermal expansion that is much higher than that of the filler 14. Thus, when a cold condition occurs, the layer of urethane 38 will allow the filler 14 to, shrink around the layer 38 in order to eliminate the stress on the filler 14.

During the period when the assembly is heated, the filler 14 tends to expand away from the insulating tube 16, but the urethane 38 with the higher coefficient of thermal expansion will expand to maintain void-free contact with the tiller l4 and the tube 16.

What is claimed and desired to be secured by Letters Patent of the United States is:

l. A fused coupler assembly for use in an underground distribution system comprising:

cial engagement with said tube and said housing. 

1. A fused coupler assembly for use in an underground distribution system comprising: a conductive grounding housing, a cylindrical tube defining a tube cartridge within said housing, a fuse element disposed within said tube, a coating helically wound on said tube, said coating being connected to line potential at least at one end and being of sufficiently low resistance to prevent corona occurring between said tube and said fuse element; and a dielectric filler in the space between said tube and said housing, said filler being in void-free interfacial engagement with said tube and said housing. 